Considering the beneficial effect of all-trans retinoic acid (ATRA) in acute promyelocytic leukemia (APL), it has been speculated that ATRA might also be useful for treating other hematologic malignancies. To test this hypothesis, we performed a dose-escalating 3-month-trial of ATRA in 15 patients with primary or secondary myelodysplastic syndromes (MDS). Morphologic diagnoses were refractory anemia (RA) in 4, RA with ring sideroblasts (RARS) in 2, RA with excess blasts (RAEB) in 7, and RAEB in transformation (RAEB/T) in 2 cases. Patients included were required to have one or more of the following criteria: transfusion- dependent anemia, pronounced neutropenia (< or = 0.5 x 10(9)/L) or thrombocytopenia (< or = 20 x 10(9)/L), or increasing blast cells in the peripheral blood or bone marrow. Therapy was started at an ATRA dose of 30 mg/m2/d, administered orally as two doses of 15 mg/m2 every 12 hours. The retinoid dose was increased to 60 mg/m2/d after 4 weeks and to 90 mg/m2/d after 8 weeks. Among 14 patients assessable for response, none obtained a complete or partial remission. Three patients had a minor response, manifested by either reduction in transfusion requirements (2 patients) or increase in neutrophil and platelet counts (1 patient). During the study period, 5 patients progressed to more advanced stages of MDS or overt leukemia. Three patients with chromosomal abnormalities receiving ATRA for a period of 10 to 12 weeks retained their cytogenetic marker after completion of treatment. Side effects of ATRA primarily affected the skin and mucous membranes, with 13 of 15 patients having at least low-grade dermatologic toxicity. In 2 cases, treatment had to be prematurely stopped because of intolerable conjunctivitis or progressive neurologic symptoms. These data suggest that ATRA has little effect on MDS. The lack of response of MDS patients, as compared with those with APL, may be attributed to the absence of the t(15;17) translocation that seems to be a prerequisite for clinical efficacy of ATRA.